This invention relates to a turbocharger for an internal combustion engine, and includes a turbine casing surrounding a turbine wheel, the turbine casing having an inlet and an outlet for the exhaust gases of the internal combustion engine and having on the inlet side, arranged substantially concentrically with the turbine wheel, a radially internal spiral path and at least one radially external spiral path, the paths having a common partition and the cross-section of the exhaust gas inlet being varied by the provision of a control element.
During operation, this type turbocharger can be adapted by varying the cross-section of the exhaust-gas inlet by the control element to therefore adapt the exhaust gas velocity in the turbine casing to different operating ranges of the internal combustion engine, for example, part-load operation or full-load operation. In such arrangement the control element is preferably actuated as a function of the charge-air pressure or of the rpm of the internal combustion engine by the provision of suitable control means.
A similar type turbocharger for internal combustion engines is disclosed in West German patent application No. 31 05 179, wherein a total of three spirals are arranged radially outwardly of internal spirals which can be unblocked and blocked individually by separate control members, and the exhaust gases flowing therethrough impinge directly upon different peripheral areas of the turbine wheel. Aside from the relatively complex and costly structure required for this type turbocharger, such arrangement possesses a significant drawback in the loss-intensive partial admission of the turbine wheel occuring with different rpms of the internal combustion engine or with varying charge-air pressures. Furthermore, the necessary control effort to be produced for the three separate control elements in order to adapt the characteristic curve of the turbocharger to the particular operating range of the internal combustion engine, is substantial.